Migrants fuel economy.

Remittances from migrant workers back to their home countries reached close to $ 232 billion last year, according to the World Bank *. This eclipsed the annual income of many nations around the world, and are an important source of external funding in many nations around the world, as the figure+ shows...
Of course, India leads the way with nearly 10% of that amount - $ 21.7 billion !

Here are the leaders...

• India : $ 21.7 billion
  
• China : $ 21.3 billion
• Mexico : $ 18.7 billion
• France : $ 11.6 billion

Here is an interesting excerpt...

Analysis of household surveys indicates that remittances have been associated with significant declines in poverty (headcounts) in several low-income countries, including Uganda (11 percent), Bangladesh (six percent) and Ghana (five percent). In addition, remittances appear to help households maintain their consumption levels through economic shocks and adversity. They are also associated with increased household investments in education and health, as well as increased entrepreneurship.

Basically, this money goes directly to the people and aid significantly in improving people's lifestyles and reducing poverty.

* - link via Sepia Mutiny
+ - figure from the above World Bank Report.